The present invention is directed to an explosive powder charge actuated device for driving fastening elements into a receiving material and includes a piston guide in which a driving piston is displaceably mounted and can be driven by the propellent gases generated when an explosive powder charge is fired from a rear firing position into a front driven position. The piston guide has a firing chamber at its rear end in which the charge is inserted and, in addition, apertures spaced apart in the axial direction of the piston guide communicate between the interior of the piston guide and a channel located between the piston guide and the housing enclosing it. In the firing position, the aperture closer to the firing chamber is closed by the piston when the piston is in the firing position.
In the known explosive powder charge actuated fastening element driving devices it is usual, after the driving stroke of the piston against the fastening element, to return the piston by mechanical force from the forward driven position into the rearward firing position. The return operation in the driving devices is cumbersome and time consuming.
To overcome this known disadvantage, an explosive powder charge actuated fastening element driving device is known from U.S. Pat. No. 3,744,240 where the return of the driving piston is effected by the exhaust gases generated by the fired charge. In this known arrangement, the energy available for the return of the driving piston is frequently insufficient to effect a complete return. Such insufficiency results from the loss of exhaust gases which occur from a channel extending along the piston guide which has axially spaced apertures which open into a front region of the guide bore in the piston guide and a rear region of the guide bore adjacent the firing chamber.